Download Lab #1 Corrosion Cells

Determining Potential Differences between Metals
Project Description:
In this lab you will directly measure the electric potential differences between metal strips in an
electrolyte. Upon measuring the potential differences you will use the data to arrange the metals in
order of electromotive force from most negative to least negative. Finally you will compare your
measured results with those listed on Page 7 of your Corrosion Control Workbook
Equipment Needed:
For this experiment you will need the following items:
1) Different strips of known metals. Different metals will be provided by your instructor and you were
asked to bring two metal samples with you to the lab.
2) Small plastic container for your electrolyte solution.
3) Standard electrolyte consisting of a saltwater solution.
4) Small alligator clips
5) Digital voltmeter and test leads
Procedure:
Step 1) Fill the plastic container three-quarters full with electrolyte solution.
Step 2) Attach the test leads to the DVM and set the DVM to measure dc voltage on the most sensitive
scale available.
Step 3) Attach the lead (Pb) sample to the red test lead. Make sure the Pb is free of oxidation prior to
use.
Step 4) Start with a second Pb sample in the black test leads then measure the electric potential
difference between the two samples on the DVM. Record the data in Data Table 1 to the nearest 0.01 V.
Continue measuring the potential differences between Pb and the other samples. Record the name of
the two additional metal samples you brought to lab and record the data in the last two cells.
Step 5) Reverse the red and black lead and repeat the measurement. Record the data in the table.
Data Table 1: Electric Potential Differences between copper and other metals
Sample metal – Red
Lead
Lead
Lead
Lead
Lead
Lead
Lead
Sample metal – Black Lead
Voltage Difference
(nearest 0.01V)
Voltage difference
(leads reversed)
Lead
Aluminum
Copper
Zinc
Steel
Student #1
________________
Student #2
________________
Lead
Step 6) Repeat these measurements with other metal samples in the Red Lead and record the data in
the Data Table 2.
Data Table 2: Electric Potential Differences Between other metals.
Sample metal – Red Lead
Sample metal – Black Lead
Aluminum
Aluminum
Aluminum
Copper
Copper
Zinc
Copper
Zinc
Steel
Zinc
Steel
Steel
Voltage Difference
(nearest 0.01V)
Analysis and Questions:
Graph the relative location of all of your metals on the line graph below starting with Pb in the center
position. With Pb attached to the RED lead plot positive voltages towards the right and negative
voltages towards the left.
Pb
-0.9
-0.5
0.0
0.5
1) Which of the metals that you have measured is MOST likely to corrode in a saltwater solution?
____________________________________________
1.0
2) Explain why this metal more likely to corrode in saltwater conditions?
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3) Which of the metals is LEAST likely to corrode in a saltwater solution? __________________________
4) Was the size of the voltage measured the same when the Pb sample was attached to the RED lead as
when attached to the BLACK lead? _______________________ (Note: the difference ___________.
This is called a voltage offset.)
5) What happened to the sign of the voltage? _______________________________________________
6) Explain why this happened?
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